Compiler bug in Build 1966
//-- This would compile instead without a message, but not execute func2() return func1()&&func2();
then, compilers usually execute only first part of Boolean expression AND if the first part is false, there is no need to execute the 2nd part.
*-In same manner, they will execute only first part of logical OR if first part is true.
Isn´t it also a major bug, that func2() is not executed in a boolean operation when the first operand is already false?
Because:
bool result=func1()&&func2();
as well as
if (func1() && func2())
would never execute func2(), while
bool result=func1()&func2()
Maybe I misunderstand your question, but if you mean this part:
then, compilers usually execute only first part of Boolean expression AND if the first part is false, there is no need to execute the 2nd part.
*-In same manner, they will execute only first part of logical OR if first part is true.
I am not sure if this is ISO standard, I know what you mean. But the problem is, that MT4 compiles an actual correct code with hundreds of warning- and also error messages.
Isn´t it also a major bug, that f
bool result=func1()&func2()
unc2() is not executed in a boolean operation when the first operand is already false?
Because:
bool result=func1()&&func2();
as well as
if (func1() && func2())
would never execute func2(), while
bool result=func1()&func2()
So, you mean only the 3rd part is a bug, right?
bool result=func1()&func2()
I don't see at as a bug, the operation is different then Boolean AND, even though you assign to a Boolean. It is a matter of further improve the optimization of compiler, but not a bug.
I am not sure if this is ISO standard, I know what you mean.
*-It's also advisable to use that to improve performance, taking into account when writing Boolean expressions to put for instance
return VarA && VarB && FuncC() && FuncD() Which might execute faster
Don't know if it's ISO or not, I just know many compilers (most I think) as well as sql compilers work the same way.
So, you mean only the 3rd part is a bug, right?
Of course not. Imho only the 3rd part is working correct. Otherwise the code needs to be always like this:
bool result=true;
result&=func1();
result&=func2();
return result;
... uhm no. 4 lines of code instead of 1 ... this can´t be meant for real.
You agree that those two statements would execute only func1() if it's false, and that is correct way to go, right?
bool result=func1()&&func2(); if (func1() && func2())*-In MT5 If func1() is true, it executes them both. Otherwise, only func1.
It's called "Short circuit evaluation", it's common in programming languages, and it's written using double && or ||.
This syntax is used to stop the evaluation when the compiler knows outcome of the boolean expression.
The real question here is why the compiler complains about the single "&".
That expression should call both functions.
Did you check MQL5 documentation on boolean operators if the MQ changed something about "&"?
- en.wikipedia.org
'&' is not a boolean operator it's a bitwise operator.
mql4 and mql5 (still beta) give the exact same warning. This is new warning and it is here to stay (with good reason in my opinion).
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New version of MetaTrader 4 build 1160
Ilyas , 2018.12.20 09:27
For group 2, we will not change behavior.
The type of binary operation is always int for operands of a smaller type.
Use
//--- This will compile with a warning message, even if the expression correct return bool(func1()&func2());However I am not sure why "bool result=func1()&func2();" doesn't give a warning in the same way, doesn't seem coherent.
It's called "Short circuit evaluation", it's common in programming languages, and it's written using double && or ||.
This syntax is used to stop the evaluation when the compiler knows outcome of the boolean expression.
Thank you, never heard about it.
The real question here is why the compiler complains about the single "&".
That expression should call both functions.
Did you check MQL5 documentation on boolean operators if the MQ changed something about "&"?
It calls both functions, but you´re not allowed to use it in a return command.
'&' is not a boolean operator it's a bitwise operator.
mql4 and mql5 (still beta) give the exact same warning. This is new warning and it is here to stay (with good reason in my opinion).
Use
However I am not sure why "bool result=func1()&func2();" doesn't give a warning in the same way, doesn't seem coherent.Thank you.
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The following code compiles in MT5 without errors, in MT4 it reports a "not boolean expression" warning - which is wrong. But when the code is changed in a way that it compiles without errors, only the half of the functions is executed.
//+------------------------------------------------------------------+
//| BoolBug.mq4 |
//+------------------------------------------------------------------+
#property version "1.00"
#property strict
//+------------------------------------------------------------------+
//| Demonstration of major bug in MT4 Build 1966 |
//+------------------------------------------------------------------+
int OnInit()
{
main();
return INIT_FAILED;
}
bool main()
{
//--- This will execute func1() and func2()
bool result=func1()&func2();
//--- This will compile with a warning message, even if the expression correct
return func1()&func2();
//-- This would compile instead without a message, but not execute func2()
return func1()&&func2();
}
bool func1()
{
Print("Function #1");
return false;
}
bool func2()
{
Print("Function #2");
return false;
}